1. Field of the Invention
The present invention relates generally to electrodes or anodes for use in the cathodic protection of metallic structures from corrosion. More particularly, the present invention relates to anodes for use in impressed current cathodic protection schemes and provides an anode that is resistant to corrosion and deterioration in use.
2. Summary of the Prior Art
Cathodic protection (CP) is a technique by which corrosion of metal surfaces is controlled by making the metal surface operate as the cathode of an electrochemical cell. This may be accomplished by placing another, more easily corroded, metal in contact with the metal to be protected to act as the anode of the electrochemical cell. The more easily corroded metal is known as a galvanic or “sacrificial” anode. CP systems are commonly used to protect steel structures or apparatus, particularly where the steel structure is subterranean or under water.
For larger structures, galvanic or sacrificial anodes cannot economically deliver enough current to provide adequate corrosion protection for the structure. In those cases, impressed current cathodic protection (ICCP) systems use anodes connected to a direct current power source that is commonly referred to as a CP rectifier. The anodes of ICCP systems typically are rod-shaped or ribbons of various specialized materials, including silicon cast iron, graphite, mixed metal oxide, platinum and/or niobium coated metals, and others. These anodes can be expensive and fragile.
Because such anodes frequently are buried in a borehole, or are exposed to seawater in an offshore application, they are subject to corrosion and deterioration. In addition to degrading the physical structure of the anode, corrosion and deterioration can cause the resistance of the anode to increase, diminishing the efficiency of the cathodic protection cell or circuit. Furthermore, in subterranean applications, common in the protection of oil field equipment and pipelines, corrosion of exotic metal anodes in ground water or soil can lead to ground water or soil contamination.
A need exists, therefore, for anodes or electrodes for use in ICCP systems that do not suffer from the disadvantages of the prior art.